1. Field of the Invention
This invention relates to improvements in a dental panoramic X-ray photographing apparatus, and more particularly to a dental X-ray photographing apparatus for entire jaws for dental diagnosis including a rotary arm having an X-ray generator disposed at one end thereof and having an X-ray film cassette holder disposed at the other end thereof in an opposed relation with each other, with an object disposed therebetween, whereby panoramic X-ray photographing can be performed as the rotary arm rotates.
2. Prior Art
A dental panoramic X-ray photographing apparatus disclosed by the Japanese Provisional Patent Publication No. 58-83939 has a function generator which determines the speed of a photographing unit to comparatively reduce the control range of X-ray tube voltage when the X-ray tube voltage is used as a dose output control value, whereby the speed pattern which ensures application of a constant X-ray dose to an X-ray film is memorized by the function generator. Although this conventional apparatus has been effective in its own way, it has the following problems to be solved.
(1) The rotation speed of the rotary arm of the apparatus is determined by the signal from the function generator. If the rotation position of the rotary arm is dislocated, however, the rotation speed of the rotary arm is changed at the dislocated position different from the regular position. If the rotation speed is decreased at the position slightly dislocated from the regular position suited to photograph the front tooth region and the X-ray dose is increased for example, the density of the image obtained on the film increases at positions different from the front tooth region and decreases at other positions. Moreover, if the rotary arm is rotated half-way and returned to its start position for some reason, the rotation speed of the rotary arm must also respond to the rotation position of the rotary arm.
(2) Since the feeding speed of the X-ray film is not compared with the X-ray transmission dose, photographing may not be performed satisfactorily due to slipage of mechanical part and the motor's follow-up errors.
(3) Since the tube current of the apparatus is not automatically controlled, the apparatus cannot follow up any great change in a tooth shape due to a lack of a bone for example.